Atomic physics

Everything is made of tiny bits called atoms.

Atoms have a center. Small parts move around that center. These small parts move in paths.

Sometimes, these small parts get more energy. This can happen from light. They might also hit other bits.

When they get energy, they jump to a new path. This is a big change.

When they move back, they let out energy. This energy can look like light.

Scientists study how these parts move and change. It is a very small world.

Atomic physics is the study of atoms. Scientists look at how atoms work as a single system. An atom has a center called a nucleus. Small parts called electrons move around this center.

Electrons stay in paths called shells. These shells are like layers around the nucleus. Most of the time, electrons stay in a calm state. This is called the ground state. But electrons can change. They can get more power from light. We call these light particles photons. They can also get power by hitting other particles.

When an electron gets extra power, it moves to a higher shell. This is called an excited state. Sometimes, an electron gets so much power that it leaves the atom. This way of changing is called ionization. If the electron falls back to a lower shell, it lets out energy. This energy often looks like a photon of light.

In 1913, Niels Bohr made a famous model. He said electrons move in fixed, circular paths. These paths are called orbits. Each orbit has its own level of energy. This helped scientists understand how atoms work.

Atomic physics is a special branch of science. It studies atoms as single, isolated systems. An atom has a center called a nucleus. Small parts called electrons move around this center. Scientists look at how these electrons are arranged. They also study how atoms interact with each other. This field is different from nuclear physics. Nuclear physics looks at the nucleus itself. Atomic physics focuses on the nucleus and the electrons together.

There is a specific way atoms work. Electrons live in paths called shells. Most electrons stay in a calm ground state. They can move to an excited state if they get energy. This energy can come from light particles called photons. It can also come from magnetic fields or collisions. If an electron gets enough energy, it leaves the atom. This process is called ionization. When an electron falls back to a lower shell, it releases energy. This energy often comes out as a photon.

Many people helped us understand these tiny things. Long ago, thinkers like Democritus studied atoms. Later, John Dalton described them as basic units. Dmitri Mendeleev created the periodic system of elements. Joseph von Fraunhofer discovered spectral lines. These lines helped scientists see how atoms behave. In 1913, Niels Bohr proposed a famous model. He showed how electrons move in fixed, circular orbits. This model helped start the field of quantum mechanics.

Scientists use many tools to study atoms today. They use lasers and magnetic fields. They also use particle accelerators and detectors. Computers help them build very large models. These models show how atoms collide and change. In the Bohr model, electrons have specific energy levels. The energy of an electron depends on its orbit. For example, an electron can jump between shells. This jump happens when it absorbs or emits energy.

Atomic physics helps us understand the big world. It provides the rules for plasma physics. It also helps us understand atmospheric physics. Even though these fields involve huge numbers of atoms, the rules are the same. Atoms in a gas spend most of their time alone. This makes it easy to study them one by one. Knowing how electrons move helps us understand chemistry. It even helps us understand how light works.

Atomic physics is a specialized branch of physics. It studies atoms as isolated systems. An isolated system means the atom is viewed on its own. Scientists look at the atomic nucleus and the electrons around it. This field focuses on how electrons are arranged. It also examines how these arrangements change over time. Atomic physics is often grouped with molecular and optical physics. It is distinct from nuclear physics. Nuclear physics studies the nucleus and its specific reactions. Atomic physics treats the nucleus and electrons as a single system.

Researchers often study atoms in isolation to understand them. This is very useful when looking at gases or plasmas. In these states, atoms spend most of their time apart. The time between interactions is very large. This allows scientists to treat individual atoms as if they were alone. Because of this, atomic physics provides the foundation for plasma physics. It also helps explain the rules of atmospheric physics. These larger fields involve huge numbers of atoms. However, the underlying atomic processes remain the same.

Electrons exist in specific arrangements called electronic configurations. They form notional shells around the nucleus. Usually, these electrons are in a stable ground state. They can move to an excited state by absorbing energy. This energy can come from magnetic fields. It can also come from colliding particles like ions or electrons. Light particles called photons can also provide this energy. There are strict selection rules for light-based excitation. However, collision processes do not follow these same strict rules.

When an electron absorbs energy, several things can happen. If it absorbs less than the binding energy, it reaches an excited state. The binding energy is the energy needed to remove an electron entirely. Once in an excited state, the electron will eventually transition to a lower state. In a neutral atom, this transition emits a photon. This occurs because energy must be conserved. If the absorbed energy exceeds the binding energy, ionization occurs. The electron is removed from its shell and sent to the continuum.

Sometimes, ionization triggers a chain reaction. If an inner electron is removed, an outer electron may drop down to fill the gap. This transition can emit a visible photon or a characteristic X-ray. Another possibility is the Auger effect. In this process, the released energy is transferred to another bound electron. This causes that second electron to also leave the atom. This effect allows a single photon to multiply the ionization of an atom.

A major breakthrough came in 1913 with Niels Bohr. He proposed the Bohr model to describe the hydrogen atom. This model combined classical physics with quantum physics. Bohr suggested that electrons move in fixed, circular orbits. These orbits are also called energy levels. He stated that angular momentum is quantized in these orbits. This means the electron can only exist in specific paths. Each orbit has a very specific amount of energy. Electrons move between these orbits by absorbing or emitting energy.

The history of this field is very long. Early thinkers like Democritus recognized matter was made of atoms. In the 18th century, John Dalton developed the modern idea of elements. Later, Dmitri Mendeleev created the periodic system of elements. The true start of atomic physics began with spectral lines. Joseph von Fraunhofer was a key figure in studying these lines. His work led to the Bohr model and quantum mechanics. This provided a new theoretical basis for quantum chemistry and spectroscopy.

Modern atomic physics has advanced rapidly since World War II. This progress is due to better computing technology. Computers allow for sophisticated models of atomic structures. New tools like lasers and particle accelerators help too. Magnetic field generation and advanced detectors also assist experimental work. These tools help scientists study both regular and chaotic processes. Today, the field continues to grow through technological advances. It remains vital for understanding the fundamental nature of matter.